This invention relates generally to rollers used in flexographic printing presses, and in particular to a bridge mandrel used to form part of the roller to allow the use of changeable sleeves in conjunction with printing rollers and to provide more durable and cost effective inking rollers.
In the flexographic printing process, a printing roller rolls a flexographic printing plate, typically made from photopolymer or rubber, over paper held on a central impression drum. The printing plate on the roller is inked by an ink roller having microfine cells saturated with ink. The presses operate at very high speeds, sometimes printing over 600 linear feet of paper per minute, which requires that the rollers rotate at very high rotational speeds. The construction of the printing roller and inking roller can vary and many different constructions have been used to attempt to optimize the printing performance of the rollers. The optimal printing roller would be durable, easy to change by one operator, provide a high quality print, maintain a high degree of concentricity, and have a low cost. The optimal inking roller would be durable, cost effective, provide good ink flow, and maintain a high degree of concentricity.
A frequently attempted method to provide such a printing roller involves the use of several layers of materials having different properties. For example, the printing roller supplied by Windmoller & Holscher for use with its Soloflex.RTM. flexographic press comprises a mandrel having compressed air conduits and an integrated cover sleeve having a microporous foam inner core and a nonporous polymeric outer surface layer. The flexible printing plates are then attached to the nonporous polymeric outer surface layer. The integrated cover sleeve is easily removed from the mandrel by using air pressure passing through the mandrel to expand the diameter of the cover sleeve. The problem with this system is that the integrated cover sleeves are quite expensive and do not last a long time or work very well because they tend to quickly lose their concentricity.
Another attempt to provide a printing roller that is easy to change by one operator, provides a high quality print, and has a low cost, involves the manufacture of the sleeves out of solid urethane. The drawback to this attempt at a solution is that it is very difficult to bore the necessary holes through the solid urethane, and the solid rollers do not maintain their concentricity very well.
Currently available inking rollers, such as those provided by Windmoller & Holscher for use with its Soloflex.RTM. flexographic presses, typically comprise a mandrel having compressed air conduits and an inking sleeve. The inking sleeve is usually a multi-layered construction with an outer layer made from ceramic having microfine cells and a porous foam inner layer. The inking sleeve is changed in virtually the same way as the printing sleeve--using compressed air. The problem with using an inking sleeve such as this is that the sleeves do not last a long time because they quickly loose their concentricity.
This invention relates to an improved roller construction and to solutions to some of the problems raised or not solved by existing roller configurations.